Let me say right off I did do some searching and I found and read the big towing thread at. That said, I've got a '07 with a dealer installed tow package, so it's got the hitch, and 4 pin wiring, also it's a Canadian truck so from my other research it's got the big battery and alternator of the factory tow package.

What I'm wondering is has anyone figured out how to hook up the factory wiring? The brake controller 4 pin harness has 4 wires, the fuse box has all the 30A fuses and the relays indicated as towing related yet the brake controller harness only has ground and the brake light pin as apparently hooked to anything. I can't find any wiring at the back under the truck either that looks like tow package beyond the existing 4 pin.

Now I have a brake controller, 7/4 pin plug, breakers and a bunch of 10ga wiring on the way to install as per the usual method but I'm just wondering if I can save some work by not running redundant wiring that's already in there somewhere and just needs to be hooked up.

Basically has anyone figured out how much wiring is missing, both into the cab then from the cab to the bumper? Especially when all the fuses and relays seem to be there.

Also, as for the tranny cooler, I plan on installing one and a trans temp guage in the near future, but for now I sometimes tow a tandem axle enclosed utility with a GTW of about 2700lbs tops which is sketchy with no trailer brakes. When we have it loaded right up we tow it with a Navigator.

I'm going thru the exact same puzzle.
My '09 (V6/stick) does not have the factory tow package.
I installed the Toyota 4pin trailer harness and relay kit,
(probably what's in yours) and a class 3 receiver (Uhaul).
While doing that I added a #10 wire in the harness bundle for the brakes in anticipation of wiring the 7 pin plug and a brake controller.
You do have room in that harness cover to un-tape it and add a wire or 2
from the trailer plug up into the lower left of the dash.
If you fool around with the trailer harness, do yourself a favor and drop the spare - 'way better access to the harness.
I am still puzzling out how much trailer brake wiring is in mine - it does have the fuse for the brakes, but I haven't yet figured out if any of the tow package wiring exists between the fuse block and the under dash.
I'll keep you posted,
Jim

What brake controller are you planning on running? I've got a prodigy P2 works great, and they make an adapter to plug it in to the factory harness. You say that there are only two wires on the factory plug, a ground and a brake light switch, are the other wires there but not connected to anything? There are two other wires that should be on the factory plug, a fused power wire and the other wire for the electric brakes.

As far as wires missing for the 7 way, there are 3, one for the electric brakes (comes from brake controller or factory plug), one power wire to charge the battery for the brake away (fuse block), and one for reverse lights (fuse block).

I don't have a wiring diagram, but you could try your local stealership (they will also have the pins you'll need for the factory plug)

Just to reiterate and clarify, I got the Hayes Toyota harness, with 4 wires and it plugs in to the 5 pin brake controller plug by the e-brake, which also has 4 wires in the right spots. The problem is only two of the wires do anything. I checked them with a multi meter and there's a brake light activation signal, and a ground, but no 12V+ from the battery and the 4th wire shouldn't do anything yet because it should run to the back.

I know on some trucks you need to plug in a relay or a fuse to 'activate' that brake controller harness but all the fuses and relays are there. So the wiring appears to be there under the dash and the fuses/relays are there under the hood which makes me wonder what's missing to activate that brake controller power.

Where I'm at now I pulled the 12V+ and brake-output pins out of the Hayes harness, I can plug the molded connector into the truck's plug to get the signal and controller ground then use some spade connectors on the other two wires to connect into my new 10ga that should be here on Saturday.

I just don't want to run a bunch of redundant wiring if it's in there somewhere from the factory. It's not all bad though, I can tap into my new 10ga charging power at the back bumper to run a back up cam or some LED bed lights.

I'm also in the process of upgrading my NON tow package '09 to handle towing with brakes.
In spite of appearances, there's no brake or charge power wiring out of the fuse box. I had the same reservations about redundant wiring.
To confirm, pull the 30A fuse from the trailer tow brake and charge
locations, look into the socket, in mine anyway, there is a hot side
contact, but nothing on the load side.
I'm in process of connecting either to the main lug or a spare spade connection inside the fuse panel, fishing the line out with the harness,
to an inline fuse, and from there in thru the firewall to the controller.
Brake stop signal is present in the under dash connector, and ground location too. When I installed the Toyota 4-pin harness I added a #10 wire going from under dash back to the 7-pin trailer plug inside the toyota add-on harness.

The brake controller will have a 4 pin plug and velcro to the dash.
Still doing that though.
Let you know how that goes.
Jim

Thanks, yes I did. I got a little carried away with a more sanitary power source than sticking a lug on the battery.
There's a few unused hot connection points inside the under hood fuse panel that are easy to get at .
No drilling or cutting needed. Just fished the wire down and out with the big harness coming out the back side.
Went with a inline fuse because I'm old school and it's more weatherproof and cleaner than one of those tin can looking breakers.
Lots of good stuff there!

I'm also in the process of upgrading my NON tow package '09 to handle towing with brakes.
In spite of appearances, there's no brake or charge power wiring out of the fuse box. I had the same reservations about redundant wiring.
To confirm, pull the 30A fuse from the trailer tow brake and charge
locations, look into the socket, in mine anyway, there is a hot side
contact, but nothing on the load side.
I'm in process of connecting either to the main lug or a spare spade connection inside the fuse panel, fishing the line out with the harness,
to an inline fuse, and from there in thru the firewall to the controller.
Brake stop signal is present in the under dash connector, and ground location too. .
Let you know how that goes.
Jim

Hey Jim could you update if you are done..am doing same thing next week..will go tody to stealership to check the fuses n wires to the dash.

Non tow package trailer wiring update....
The only thing I got from the dealership is the 08921-04960 trailer lighting
harness. Since I bought the truck from them they give me a 15% discount on parts. This is better than the Hoppy adaptor because it adds another fuse and blinker relay. Before installing however, I un taped the harness and sneaked in a 10 gauge wire to carry the brake control output,and re-taped the harness. In hindsight i should also have added another for camper charging too. I spliced into the back end of this harness to power the 7 pin trailer plug. If you go this way , do remove the spare to ease wire routing.
Contrary to all the info on this site and elsewhere, in my truck there's no
blue wire for brake signal in the bogus "factory" brake control connector under the left side of the dash. There is a very light gauge wire in that connector that does go hot with the brake lights. I used this to signal the brake controller. Scary thin wire though.
I ran power for the brake controller from inside the underhood fuse box,
(flat spade connector on one of the unused 30A breaker sockets) and to a weatherproof 30A fuse holder on the left inner fender, and thru the wiring boot to the brake controller under dash. I velcroed the controller in place and installed an in line connector plug so I can remove it painlessly.
So far works well.
If you need more info let me know.
Jim

Jim, Check the pict i put..where i pointed the Towing tail, stop light cntrl as per the diagram on the panel cover. Whereas you hav taken a source frm a different area..? Any reason why.?
Also How do i check to see if that point is receiving power.? How did you manage to take the output.? Thnks.

I'm a little confused about exactly what your question is but here goes....
The Toyota harness kit (08921-04960) will get your turn/stop/tail lighting
to the rear bumper with the flat 4 pin connector. It also adds a "Towing Tail" fuse and relay in the "Towing Tail" sockets of the panel - see my picture. This is the lighting source. Unfortunately it does nothing for an electric brake control.
You still need a separate 20 or 30 Amp source for the brake control
and a brake on/off signal source.
I sourced the brake controller power from the unused 30A flat connection inside the fuse panel instead of connecting directly from the battery just because it's cleaner, but not easier....
This runs thru a fuse and into the brake control unit I installed under dash.
Look closely at the front side of the rubber fitting where the wiring goes through the firewall - mine had an un used nipple that made for easy pass thru that's water tight.
The brake on/off signal is from that connector already under the dash.
A meter or light bulb will enable you to verify 12v on a connector or fuse socket, but in my case there was NO contact or wire on the load side of the 30A "TOWING" fuse position, making it useless .
Hope this clears it up, if not PM me again I'll try to help.
Jim

Thnks jim, am gonna try out tommorw..but now i wonder if i will see power coming up at the brake on/off signal lead..as i dont have the TOWING TAIL fuse in the panel. Could you give me the part no of that Towing tail fuse..so if i dont have voltage there i will run to toyota and get that part.
Thnks

With the assistnce frm the company tech whre i bought the 7pin adapter kit..i installed the kit...I am seeing ..
Voltage @ 9 oclock - Left turn
Voltage @ 3 oclock - right turn
Voltage @ 5 oclock - SUPPOSED TO BE Ground
No Voltage @ 11 o clock - Charging circuit.
I did run a 30Amp pwr wire, Got hold of that skinny thin blue BRAKE SIGNAL wire n connected to the B/C blue wire.
When you dont have trailer connected DO YOU STILL SEE VOLTAGE @ 7 OCLOCK WHILE APPLYIN BRAKES..??
Here s is the product i used...http://www.towready.com/content/prod...55&part=118799

You connected the light gauge brake signal wire in the truck's harness to the blue wire on the brake controller? If you did that's wrong. The small gauge wire on the truck side that goes hot with the brake pedal depressed should go to the red wire on the brake controller. All it does is send a heads-up signal to the brake controller. The blue on the brake controller is the heavy gauge high amp output to the brakes on the trailer.